The mass air flow sensor on a 1997 Nissan pickup XE is of the “hot wire” types: The vehicle's computer heats the wire to a predetermined temperature and then maintains it; in order to maintain the temperature, the computer must vary the voltage in accordance with the changes in the air volume. The computer uses this voltage variance to determine engine load and to calculate ignition and fuel injection timing. There are several tests and symptoms to determine MAF sensor failure.
Recognize the symptoms of a MAF sensor failure. A 1997 Nissan truck experiencing a MAF sensor failure will not operate over 3,000 rpm. The computer will go into a failsafe mode and modulate the fuel injectors to limit the rpm. The computer will also turn the "check engine" light on and set a code for the MAF sensor. The 1997 Nissan truck also has a problem with the ground on this sensor. This poor ground causes not only driveability issues, but it will also set false codes indicating an oxygen sensor failure and fuel injector leaks.
Locate the MAF sensor on the passenger's side of the engine, leading to the throttle body. Look at the electrical plug closely. On close inspection, notice that there are three wires in a straight row, but four terminals. The lead terminal on one side is vacant. Next to the empty terminal is the power supply wire: the middle wire is the ground and the last wire on the opposite side is the signal wire.
Connect the black voltmeter lead to a good ground on the intake manifold. Use the red lead to probe the last outside wire, or signal. Do not disconnect the plug; use the pointy end to pierce the wire. Have a helper start the truck. Watch the voltage as the helper slowly raises and lowers the rpm. The voltage should rise smoothly and drop with the rpm. If it doesn’t, the signal is bad.
Have the helper snap the throttle a couple of times while you watch the voltmeter closely. The voltage should climb as rapidly as the throttle is snapped, and return equally as fast. Before condemning the sensor, do one more test. As mentioned earlier, this particular truck has problems with the sensor's ground.
Move the red probe from the sensor signal to the middle ground wire. With the engine running at an idle, the voltmeter must read .10, or a tenth of a volt. If the reading is anything other than this value, the ground is suspect. Add an additional 16-gauge wire to the existing ground wire. Remove some of the insulation on the wire at the connector and solder this additional wire to the present one. Attach the other end of the wire to the intake manifold. You will be back in business with the extra ground.
